1. Field of the Invention
The present invention is generally concerned with an improved flotation apparatus and process for purifying a waste effluent by forming a separable, buoyant floc out of the waste matter suspended in the effluent. The invention utilizes a novel floc barrier and current diverting means in the flotation tank to facilitate the removal of buoyant floc out of the tank.
2. Description of the Prior Art
Purification of waste effluents by flotation devices is well known in the prior art. In general, such devices purify effluents such as waste water by forming a buoyant floc out of the particles suspended in the water. The buoyant floc rises to the surface of the water, where it is skimmed off by an arrangement of skimming paddles. More specifically, the stream of effluent to be treated is first mixed with one or more conditioning agents and then conducted into a flotation tank. In the flotation tank, the effluent and conditioning agent are mixed with a stream or cloud of small bubbles of buoyant gas. The conditioning agent may be a precipitating agent, a coagulating agent, a flocculating agent, or function to change the pH of the effluent. The conditioning agent causes the particles of waste matter suspended in the effluent to flocculate into agglomerates of ever-increasing size. Since this flocculating process is carried out in the presence of the stream or cloud of tiny, buoyant bubbles produced in the flotation tank, some of these bubbles become entrapped in the growing agglomerates of floc. The entrapped bubbles of buoyant gas accordingly render the agglomerates of floc buoyant, and cause them to float up to the surface of the flotation tank. There, the buoyant floc is swept or raked by the paddles of a skimming mechanism into a floc collection area in the tank, where it is ultimately raked out of the tank. The treated effluent flows into a discharge region of the tank, where it flows out through an outlet.
Ideally, a flotation device should be capable of effectively purifying a large volume of effluent in as short a time and as small a volume as possible in order to minimize the expenses associated with both the construction and space requirements of the device. However, one problem which arises when one attempts to increase the effluent-purifying capacity of existing devices has been the tendency for the buoyant floc to stray from the floc collection area of the tank over to the area of the tank where the treated effluent is discharged. Such floc-straying may be caused either by the fluid currents generated by the inflow of the effluent stream into the tank, or by the natural tendency of the buoyant floc to attempt to randomly distribute itself over the surface of the tank, or by both of these effects. Stray floc can mingle with and foul the treated effluent and thereby impair the effectiveness of the device. Thus it would be very advantageous if the flotation device were capable of both quickly and effectively sweeping the buoyant floc toward the floc collection region of the tank, thereby keeping it away from the outlet region of the tank. Such a feature would increase the effluent-purifying capacity of the tank and ensure that only a minimal amount of buoyant floc, if any, would stray into the discharge region of the tank where it could inadvertently be discharged out of the tank along with the purified effluent.
Prior art flotation devices have generally employed an array of chain-driven skimming paddles to sweep the floc into a floc collection region of the tank, where it is in turn raked up a shallow ramp and expelled over the edge of the tank. Such skimming mechanisms generally utilize a plurality of parallel skimming paddles which are continuously moved in the same direction across the tank surface by a pair of parallel chains driven by sprockets. While these mechanisms are generally effective in performing their intended function, they still fall short of an ideal performance. Buoyant floc can still pass under the paddles, leaving some in the outlet region of the tank. If the paddles are simply made deeper in an attempt to solve this problem, they can generate so much surface turbulence in the water that the tiny bubbles entrapped in the agglomerates of floc are shaken out, thereby rendering the floc non-buoyant. Such non-buoyant floc sinks to the bottom of the tank, where it must be removed either by way of a floor raking mechanism, or by way of troublesome and time-consuming maintenance procedures. Furthermore, such mechanisms do not provide a positive means for preventing the floc from straying once it is collected in the floc collection region of the tank. Hence it is possible for the floc collected by the paddles to stray into the purified effluent discharge area. Clearly a need exists for a mechanism which would substantially improve the effectiveness of the skimming operation in flotation devices.